Project Summary/Abstract Pathological angiogenesis is a key process that drives vascular remodeling in numerous cardiovascular and metabolic diseases including diabetic retinopathy, age-related macular degeneration (AMD) and cancer. However, owing to scarcity of proper molecular targets, it is widely recognized that hindering pathological angiogenesis to mitigate these deleterious disease conditions remains daunting. Our long-term goal is to uncover original molecular mechanisms and identify fresh molecules that prevent pathological angiogenesis in hopes of offering potential new therapeutic approaches. In our last funding cycle, we examined the role of endothelial epsins and Dab2 in reciprocally regulating VEGF signaling and created mice with either inducible endothelial-specific epsins 1 and 2 deficiency (EC-iDKO) or endothelial-specific Dab2 deficiency (EC- Dab2iKO). We showed that epsins and Dab2 interact with VEGFR2 via a mutually exclusive mechanism. Interestingly, mice lacking endothelial epsins and Dab2 (EC-iTKO) rescue heightened angiogenesis caused by epsins depletion, or attenuated angiogenesis produced by Dab2 loss, suggesting that epsins and Dab2 antagonizing each other to modulate VEGF-mediated angiogenesis in vivo. Given that VEGF signaling plays a central role in normal, as well as pathological angiogenesis, how epsin and Dab2 are differentially recruited to mediate VEGFR2 internalization and modulate VEGF signaling is a highly significant and open question. In searching for upstream signals that preferentially trigger either epsin or Dab2 binding to VEGFR2, our latest study revealed that Sphigosine 1 Phosphate (S1P) stimulation facilitates epsins but hinders Dab2 binding to VEGFR2, leading to VEGF-induced VEGFR2 degradation. How S1P selectively allows the recruitment of epsins to VEGFR2 is poorly understood. Further, we discover that miRNA (miR-19) directly binds epsins' 3'UTR and represses epsins' expression. Whether miR-19 potentiates VEGF signaling by inhibiting epsins' expression is entirely unclear. Given crucial roles epsins play in regulating angiogenesis, uncovering molecule mechanisms and genetic modifiers that control epsins' activity and govern epsin expression may offer new therapeutic approaches in pathological angiogenesis. To this end, we hypothesize that S1P induced Src activation phosphorylates VEGFR2, enabling VEGFR2:Cbl association and VEGFR2 ubiquitination, and enforcing epsin:VEGFR2 binding and VEGFR2 downregulation. We further hypothesize that epigenetic regulation including miR-19 that directly suppresses epsins' expression, causing heightened VEGF signaling. We will utilize multifactorial approaches to investigate molecular mechanisms responsible for regulating epsin's activity and expression. Lastly, we will determine therapeutic potential of enhancing epsin or S1P function in pathological angiogenesis. If fruitful, our findings will advance our understanding of novel pathways and targets that modulate VEGF signaling, offering a new class of therapeutic strategies, and inaugurating a paradigm shift in research of pathological angiogenesis to fight devastating diseases including AMD, cancer and diabetes.